Pitot static tester



Jan. 30, 1968 1 H ANDRESEN, JR Y 3,365,928

PITOT sTATIc TESTER l Original Filed May 17, 1962 5 Sheets-Sheet 1 /7 Qf 6D Q 27 a V K lo,

a jx Z /l 35 3a /Z l 32 33 y INVENTOR.

Jan. 30, 1968 J. H. ANDRESEN, JR 3,365,928

PITOT STATIC TESTER Original Filed May 17, 1962 5 Sheets-Sheet E FIF-.E.

.Suf/Y INVENTOR. J/WV M0/675.29%@

Jan# 30, 1968 J. H ANDRESENY, l 3,365,928

PITOT STATIC TESTER United States Patent O 3,365,923 PlTT STATIC TESTERlohn Henry Andresen, dr., Hewitt, NJ., assigner to IntercontinentalDynamics Corporation, Englewood, NJ., a corporation of New York Originalapplication May 17, 1962, Ser. No. 196,042, now Patent No. 3,243,990,dated Apr. 5, 1966. Divided and this application Aug. 23, 1965, Ser. No.llLSZl ti Claims. (Cl. 73--4) ABSTRACT F THE DISCLGSURE An apparatus fortesting and calibrating air speed indicators, machmeters, altimetersetc. is provided with a static manifold and a pitot manifold forappropriate connection to the indicator to be tested. A single pump isconnected between the manifolds to maintain the pitot manifold at ahigher pressure than the static manifold. Means are provided to bleedair from the atmosphere into the static manifold, from the pitot to thestatic manifold and rom pump output to the atmosphere, each in acontrolled manner to maintain the pressures therein at the proper levelfor testing purposes.

This application is a division of copending application Serial No.196,042, tiled May 17, 1962 and relating to instrument testing deviceshaving variable pressure systems and is an improvement over the deviceset forth in U.S. Patent No. 3,089,331, issued May 14, 1963.

The testing of air data instruments such as altimeters, airspeedindicators, maohmeters, and the like requires an absolute pressure and ahigher pressure differing from this absolute pressure by a regulatedcontrolled amount. Thus, test instruments of this type include a staticmanifold which is connectable to the static pressure port of an aircraftand a pitot manifold which is connectable to the pitot inlet port of theaircraft. ln the device of the aforesaid U.S. Patent 3,089,331, a firstpump is provided to establish the pressure Within the static manifold,with this pressure being either above or below ambient depending uponthe conditions which are to be simulated. An electronic servo meanswhich operates a control valve maintains pressure within the staticmanifold at the required level. A second pump is provided to establish apressure in the pitot manifold which is referenced to, and is alwaysgreater than, the pressure within the static manifold though notnecessarily greater thanl ambient. Additional electronic servo meansoperates another control valve to maintain a selected differentialpressure between the static and pitot manifolds.

The instant invention provides a novel means whereby it is necessary toutilize only a single pump to create pressures in both the static andpitot manifolds. This is accomplished by providing a pressure supplyvalve which acts to store up the eiuX of the pump and establish apressure in a chamber of the valve which is at some arbitrary amounthigher than the pressure within the pitot manifold. Should pressurewithin the chamber exceed this arbitrary amount a relief valve openspermitting the eX- cess air to bleed to ambient. The pitot manifold isconnected to the valve chamber through a needle valve which acts as arestriction to the flow of air from the chamber to the pitot manifoldwith the needle valve permitting only enough air to ow to cause thepitot pressure to increase at some desired minimum rate of change of airspeed. When the pitot pressure rises so that the differential pressurebetween the pitot and static manifolds exceeds the desired pressure thedifferential servo pressure controller operates its associated controlvalve so that the latter j assauts Patented Jan. 30, 1968 ICC opens justenough to maintain the desired differential pressure.

ln the device of the aforesaid U.S. Patent No. 3,089,331 in order toestablish a pressure within the static manifold greater than ambient notonly was it necessary to adjust the altitude selector control but it wasalso necessary to adjust the position of a selector valve. Thus, it wasnecessary to make two adjustments.

The instant invention eliminates the necessity for the selector valve byutilizing an arrangement which includes the pressure suply valvepreviously mentioned and in addition utilizes an air supply controlvalve and a needle valve connected between the static manifold and theinput to the pump.

Thus, when the static manifold is to be at a pressure near or greaterthan ambient this pressure is supplied from the air in the chamber ofthe pressure supply valve. When the static manifold is to be at apressure below ambient there will be a iow of air from the staticmanifold through the needle valve to the input of the pump causing apressure drop across this needle valve. This drop causes the air supplyvalve to admit some ambient air to the pump inlet. This air passesthrough the pump and through the control valve causing the pressure'within the static manifold to rise above ambient by the amount of thedrop across the needle valve. This arrangement makes it possible toobtain controlled pressures which are very close to ambient while in theprior art it was dilicult to control the drop across the static controlvalve so that it was difficult to regulate pressures close to ambientwhether these pressures were above or belovt ambient.

In the prior art devices of the type under consideration it has oftenbeen desirable to generate a pressure which is modulated about a tiredpoint. Typically this is done by operating a bellows through a crank pindrive bringing about a pressure change in accordance with the volume 0fchange of the bellows. This has proved less than satisfactory in thatthe center value of the modulated pressure is subject to drift and theamplitude of the pressure modulation is diticult to establish. The driftof the center value of pressure is caused by leakage anywhere in thesystem, temperature changes in the trapped air, and changes in volume ofthe system under test. Modulation control is difficult since it dependsupon the stroke of the bellows, the value of the center pressure, thevolume of trapped air including the air in the system under test, andthe geometry of the various restrictions to iiow in the system.

The instant invention overcomes these dimculties by utilizing a staticcontroller which includes a differential transformer whose outputreaches a null when the static manifold is at a desired center value ofpressure. In addition, the rotor of a synchro is continuously rotated toproduce an output which is summed in phase or out of phase with theoutput of the differential transformer. The combined outputs of thesynchro and differential transformer produce a modulated signal which isamplitied and utilized to operate the static control valve to producethe desired pressure modulation.

Accordingly, a primary object of this invention is to provide a novelconstruction for a pitot static tester.

Another object isto provide a tester of this type which requlres but asingle pump to establish both static and pitot pressures.

Still another object is to provide a novel pitot static tester havingsimplified controls for producing an accurately controlled pressureWithin the static manifold which is either above or below ambient.

A further object is to provide a novel means for producing pressuremodulations.

A still further object is to provide a novel pressure modulating -meansincluding a differential transformer for establishing the centerpressure value and a synchro device for producing the modulations aboutthis center value.

These as well as other objects of the instant invention shall becomereadily apparent after reading the following description of theaccompanying drawings in which:

FIGURE 1 is a schematic of a pitot static tester constructed inaccordance with the teachings of the instant invention and utilizing asingle pump for establishing pressures within both the static and pitotmanifolds.

FIGURE 2 is a schematic of a portion of a pitot static tester includingmeans constructed in accordance with the teachings of the instantinvention for modulating the pressures within the static manifold.

FIGURE 3 is a graph illustrating the output voltage of the synchro inthe device of FIGUR-E 2.

FIGURE 4 is a schematic illustrating a portion of a pitot static testerincluding means for establishing pressures either above or below ambientwithin the static manifold by setting merely one control.

Now referring to the figures and more particularly to FIGURE l. It isnoted that the pitot static tester illustrated in FIGURE l isessentially the tester illustrated in FIGURE 2 of the aforesaid U.S.Patent No. 3,089,331 except that the latter includes individual pumpsfor the static and pitot manifolds while in the instant invention only asingle pump is required.

The intake of air pump 11 is connected through conduit 12 to staticmanifold 13 with the latter being connectable through conduit 14 and asuitable connector, well known to the art, to the static port of anaircraft or to an instrument on a test bench. Static manifold 13v isconnected to ambient through normally closed static control valve 15.Static controller 16 acting through amplier 17 controls the operation ofstatic control valve 15. Controller 16 is connected through conduit 13to static manifold 13 and compares the static pressure to pressurewithin a standard capsule (not shown) and the desired pressureestablished by the setting of control 19. For a reason to be hereinafterexplained, controller 16 is also connected to normally closed pitotsupply solenoid valve 21 for operation of the latter. The altitudesetting corresponding to the pressure within static manifold 13 is readfrom the face of altimeter 22.

Pitot manifold 23 is connectable through conduit 24 and suitablefittings `(not shown) to the pitot port of the system to be tested.Airspeed indicator 25 is connected between the static and pitotmanifolds 13, Z3 so as to produce a reading indicative of thedifferential pressure between these manifolds. Differential pressurecontroller 26 is connected between static and pitot manifolds 13, 23 andis constructed to compare the difference between pitot and staticpressures with a pressure setting obtained by the manipulation ofcontrol 27. The amount by which this pressure difference differs fromthe setting of control 27 creates an error signal which is fed throughamplifier 23 to open normally closed differential pressure control valve29 connected between the static and pitot manifolds 13, 23. It is notedthat when the differential pressure is too high control valve 29 isopened permitting enough air to bleed from pitot manifold 23 to staticmanifold 13 to establish the desired pressure difference.

The output of pump 11 is connected to chamber 31 of pressure supplyvalve 30. Valve 31B includes diaphragm 32 separating chamber 31 fromanother valve chamber 33 which is connected directly through conduit 34to pitot manifold 23. Diaphragm 32 carries valve seat 34 which is biasedby spring 35 within chamber 33 toward end 36 of conduit 37 whose otherend 38 is connected to ambient. Conduit end 36 is disposed withinchamber 31 and is closed by spring 35 which tends to hold valve seat 34against conduit end 36. The output of pump 11 is connected throughsolenoid valve 21 in series with needle valve 39 to pitot manifold 23.

Pump 11 creates a partial vacuum in static manifold 13. This vacuumbeing controlled to a selected value by static control 16, amplifier 17and static control valve 15. Valve spring 35 is chosen so that valveseat 34- closes conduit end 345 until such time as the pressure withinvalve chamber 31 exceeds, by predetermined amount, the pressure withinpitot manifold 23. Typically this pressure is in the order of 15 I-Ig.For higher pressures within chamber 31, diaphragm 32 is operatedupwardly thereby raising valve seat 34 and permitting the excess airbeing delivered by pump 11 to be conducted through conduit 37 toambient. Thus, it is seen that chamber 31 constitutes a reservoir forair at a pressure in excess of pitot pressure.

Air delivered by pump 11, when solenoid valve 21 is open, goes through aneedle valve 39 to pitot manifold 23. Valve 39 acts as a constriction tothe flow of air into pitot pressure to increase at some desired minimumrate of change of air speed. When the pressure within pitot manifold 23rises so that the differential pressure between the static and pitotymanifolds 13, 23 exceeds that set by control 27 of differentialpressure control Z6, controller 26 acting through amplifier 28 opensdifferential pressure control valve 29 just enough to maintain thedesired differential pressure.

It is noted that when the set differential pressure is established, allair entering pitot manifold 23 must go through differential controlvalve 29 to static manifold 13. lf at this time pump 11 is trying toraise the vacuum in static manifold 13, air from pitot manifold 23causes a loss in the rate of evacuation. This is undesirable. Thus,pitot supply solenoid valve 21 is present. Solenoid valve 21 isdeenergized, hence closed, whenever static control valve 15 is closedand hence is acting to produce higher vacuum at maximum rate withinstatic manifold 13. With solenoid valve 21 closed the output of pump 11is prevented from entering pitot manifold 2.3 thereby minimizing airflow through differential pressure control valve 29 so that the fullcapacity of pump 11 is made available for evacuating static manifold 13.

Now referring more particularly to FIGURES 2 and 3. The elements of theFIGURE 2 schematic corresponding to similar or identical elements of theFIGURE l schematic are given identical reference numerals. FIG- URE 2discloses a novel means for modulating the pressure within staticmanifold 13.

Static controller 16 includes differential transformer 4t) havingE-shaped core 41 and armature 42. The position of core 41 is changedthrough the operation of knob 19 to establish the center value ofpressure about Vwhich the modulations will take place. The centralportion of armature 42 is mounted to one end of lever 43 which ismounted at a point intermediate the ends thereof to fixed pivot 44. Link45 connects the other end of lever 43 to evacuated, flexible diaphragmcapsule 46.

The primary winding 47 and two secondary windings 43, 49 of differentialtransformer 40 are mounted to core 41 with terminals 47a, 47b of primary47 being connectable to an appropriate A.C. supply. As is well known tothe art, the position of armature 42 relative to core 41 infiuences thecoupling between primary 47 and secondaries 4S, 49 thereby influencingthe voltages induced in each of the secondaries 4S, 49. secondaries 48,49 are connected in series opposing relationship from ground throughresistor 50 to the input of amplifier 17.

As previously explained, pump 11 is continuously evacuating staticmanifold 13. When the vacuum Within manifold 13 reaches the value set byknob 19, differential transformer 4f) produces a null output since link45 and lever 43 have appropriately positioned armature 4Z relative tocore 41. Further vacuum increase causes differential transformer 49 toproduce an output whose amplitude is lproportional to and of oppositephase to -that which it produced at vacuums below the null. Thus, thecombined output of secondaries 4S, 49 produce a signal which is fedthrough resistor 5t) toamplier 17. The latter is sensitive only to theopposite phase so that this signal is amplified and energizes theproportional acting solenoid control valve 15 to let just enough airleak into static manifold 13 to maintain the vacuum at the set value.

To produce a sinusoidal modulation, switch 51 is closed therebyenergizing rotor winding 52` of synchro 55 with the latter beingcontinuously operated by synchro motor 53 acting through gear train 54.Terminal 52a of rotor winding 52 is connected through switch 51 to themovable arm 56 of potentiometer 57 while terminal 52b is connected toone end of potentiometer 57. Potentiometer 57 is connected across the AC. supply which energizes the differential transformer primary winding47. The voltage across the rotating rotor winding 52 induces voltages inthe synchro stator windings 58-60 with windings 58 and 59 beingconnected in series from ground through resistor 61 to amplifier 17.Additional resistor 62 is connected from ground to amplifier 17.

Assuming that controller 16 is holding the vacuum within static manifold13 at some set value, there will be a small voltage from windings 48, 49which is amplied and acts to hold valve 15 open. Now as a voltage fromsynchro 55 is introduced this voltage will immediately open or closevalve 15 depending upon the phase of the synchro output voltage at thetime it is introduced (see FIGURE 3 for synchro output voltage). Thepressure within static manifold 13 will change causing `the output ofcontrol windings 48, B9 to change in a direction to cancel the effect ofthe voltage introduced by synchro 55. The voltage from controller 16varies linearly with pressure over small excursions so that changes inpressure will be proportional to changes in voltage from synchro 55thereby producing a sinusoidal pressure variation about the pressureexisting before the synchro voltage was introduced.

The amplitude of modulation is determined by the values of resistors 50,61 and 62 and by the setting of potentiometer wiper arm 56. Itis to beunderstood that the latter will have a calibrated dial operated inunison therewith. The output of the two wires of the synchro stator is avoltage of supply frequency which is modulated in a sinusoidal manner.

It is noted that not only controlled oscillations of sinusoidal form butany pattern of pressure change (within the proportional signal outputrange of the controller) can be affected by introducing an A.C. voltageof suitable amplitude either in phase or 180 out of phase with thecontrol output. For example, the outputs of an analog computer which arevoltages simulating altitude and air speed of a ertain iiight maneuvermay be inserted resulting in the simulated altitude and air speedchanges of this maneuver being generated by the tester. In addition, auniformly changing voltage can be introduced to give a uniform rate ofchange of static or pitot pressure. A variable speed gear train orseveral different gear trains and sync-hres may be used to obtain morethan one frequency of modulation.

It is also noted that valve 15 is a proportional valve rather than avalve of the type which is either closed or fully open. As explained indetail in the aforesaid U.S. Patent No. 3,089,331, the extent to whichvalve 15 opens is controlled by the magnitude of the error signal. Theutilization orf a `proportional valve, rather than an on-oif valve,enables the device of the instant invention to have a rapid, smoothresponse and permits multiple forms of modulation to be imposed on thecorrection signal.

Now referring more particularly to FIGURE 4 which illustrates amodification of the constructions shown in FIGURES l and 2. With themodification illustrated in FIGURE 4, it is possible to obtain controlpressures either above or below ambient in the static manifold 13 bymerely manipulating the single adjustment control 19 of staticcontroller 16. This is accomplished by providing needle valve 71 inconduit 12 which connects the intake of pump 11 to `static manifold 13.Further, air supply control valve 70 is provided between static manifold13 and the intake of pump 11.

Air supply control Valve 7 t) includes diaphragm 72 and partition 73which cooperate to define chamber 75 within valve housing 74. Chamber 75is in direct communication with the intake of pump 11. Partition 73 is-provided with a central opening which is normally closed by valve seat76 biased to closed position by spring 77. Typically, spring 77 ischosen such that its force is overcome When there is a pressure of fromone to two inches of mercury acting upon diaphragm 72. Rigid link 78connects valve seat 76 to diaphragm 72 so that when the latter isdeliected downward, valve seat 76 will be moved downward against theforce of biasing spring 77 and the central aperture of partition 73 willbe open. Under these circumstances valve chamber 75 is connected tobottom valve chamber 79 which is at ambient. The portion of valvehousing 74- above diaphragm 7 2 is connected through conduit 81 directlyto static manifold 13.

It is noted that the pressure within chamber 31 of pressure supply valve30 is above pitot pressure which is always above static pressure orsuiiiciently above ambient pressure so that pressure within chamber 31will be above static pressure even when static pressure is somewhatabove ambient. In the embodiment of FIGURE 4, static control valve 15instead of being connected from static manifold 13 to ambient isconnected from static manifold 13 by conduit S2 to chamber 31.

When static controller 16 is set to establish a pressure below ambientthis pressure can be established in the normal manner and regulated byoperating static control valve 15 to admit controlled amounts of airfrom pressure supply valve chamber 31 to static manifold 13. However, ifthis air is to raise the pressure in the static manifold 13 more airmust be lead in through static control valve 15 then is being drawn outby pump 11. lf air supply control valve 70 were not present, chamber 31could supply more air than was being drawn from static manifold 13.

So long as there is a flow of air evacuating static manifold 13 therewill be a pressure drop across needle valve 71 so that the pressurewithin valve chamber '75 is less than that within static manifold 13.Under these conditions diaphragm 72 is moved downward moving valve seat76 downward thereby opening the valve. rfhis permits a certain amount ofambient air to enter pump 11 so long as pump 11 is sucking a vacuumwhich is below ambient pressure.

In the situation where controller 16 is acting to establish a staticpressure above ambient, static control valve 15 opens and admits acopius supply of air into static manifold 13. Pump 11 in evacuating thisair through needle valve 71 causes a ipressure drop across this needlevalve 71 thereby enabling air supply control valve 70l to open andconnect the intake of pump 11 to ambient. Under these circumstances thestatic pump end of needle valve 71 is at ambient and the static manifoldend of valve 71 is above ambient, hence static manifold pressure isabove ambient. In this manner static pressure may be controlled at avalue above ambient.

Thus, this invention provides a novel construction for a pitot statictester which includes novel means for obtaining controlled modulation ofair pressure about a fixed reference. The static controller alsoincludes novel means for obtaining and regulating both static pressureand pitot pressure by utilizing only a single pump and further providesnovel means `for producing a static pressure which is either above orbelow ambient pressure by merely adjusting a single control. It isobvious that any desired combination of these features may be combinedin a single tester.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now be apparent tothose skilled in the art.

'7 Therefore, this invention is to be limited, not by the specificdisclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

l. A device of the class described comprising a first and a secondmanifold; pump means for establishing a first and a second pressure insaid first and said second manifolds, respectively, with said secondpressure exceeding said first pressure; first servo means formaintaining said rst pressure referenced to a standard; second servomeans for maintaining said second pressure referenced to said firstpressure; said pump means including an intake and an output; first meansconnecting said intake to said rst manifold and second means connectingsaid output to said second manifold; a valve including a chamberconnected to said output Iby said second means and constructed to permita third pressure exceeding said second pressure and referenced theretoto build up in said chamber.

2. The device of claim l in which the second means includes aconstricting means positioned between said second manifold and a commonfunction connecting said output to said chamber for regulating maximumflow rate from said pump means to said second manifold.

3. A device of the class described comprising a first and a secondmanifold; pump means for establishing a first and a second pressure insaid first and said second manifolds, respectively; first servo meansfor maintaining said first pressure referenced to a standard; secondservo means for maintaining said second pressure referenced to saidfirst pressure; said pump means including an intake and an output; firstmeans connecting said intake to said first manifold and second meansconnecting said output to said second manifold; a valve connected tosaid output by said second means and constructed to permit a thirdpressure to build up therein which is referenced to said secondpressure; said second pressure exceeding said first pressure and saidthird pressure exceeding said second pressure; said second means alsoincluding a supply valve positioned between said valve and said secondmanifold; an operative connection from said first servo means to saidsupply valve to control operation of the latter such that the supplyvalve is closed whenever said first servo means is operating to lowerpressure in said first manifold.

4. The device of claim 3 in which the second pressure exceeds the rstpressure and the third pressure exceeds the second pressure.

5. A device of the class described comprising a manitfold; pump meansfor establishing a pressure within sai-d manifold; a servo means formaintaining said pressure at a predetermined level; said pump meansincluding an intake and an output; a constricting means connectedbetween said manifold and said input; and valve means responsive to apressure drop existing across said constricting means for connectingsaid intake to ambient when pressure at said intake is in excess of apredetermined magnitude less than pressure in said manifold.

6. The device of claim 5 in which the valve means comprises a chamberconnected to said intake; said chamber partially dened by a first walland a second wall; said first wall comprising a movable portionsubjected to said pressure in said manifold; said second wall includingan aperture, a valve member for normally closing said aperture; meansconnecting said movable portion to said valve member whereby saidaperture is opened whenever the pressure within said chamber is at leasta predetermined magnitude below pressure in said manifold.

7. The device of claim 5 also comprising a connecting means between theoutput of said pump to said manifold; said connecting means comprising acontrol valve constituting a portion of said servo means.

8. The device of claim 6 also comprising a connecting means between theoutput of said pump to said manifold; said connecting means comprising acontrol valve constituting a portion of said servo means.

References Cited UNITED STATES PATENTS 5/1963 Sharko et al. 73-4 8/1966Shank 73-4

